Power modules including power chips (semiconductor devices) mounted thereon, such as insulated gate bipolar transistors (IGBTs) and metal oxide semiconductor field effect transistors (MOSFETs), are used as switching devices that perform the switching operation of energizing and interrupting a current speedily.
The continuous switching operation causes the power loss being the integral of the product of the current flowing through the switching device and the voltage applied to the switching device, resulting in the heat generation in the power chip. If the temperature of the power chip exceeds the guaranteed range of operation, the power chip would malfunction.
To prevent the temperature of the power chip from exceeding the guaranteed range of operation, the power chip including a temperature sensing diode that monitors the surface temperature of the power chip has been used (see, for example, Patent Documents 1 to 3).